A display apparatus of a PDP and a DMD makes use of a subfield method, which has binary memory, and which displays a dynamic image possessing half tones by temporally superimposing a plurality of binary images that have each been weighted. The following explanation deals with PDP, but applies equally to DMD as well.
The PDP subfield method is explained using FIGS. 1, 2, 3.
Now, consider a PDP with pixels lined up 10 horizontally and 4 vertically, as shown in FIG. 3. Assume that the respective R,G,B of each pixel is 8 bits, the brightness thereof is rendered, and that a brightness rendering of 256 gradations (256 gray scales) is possible. The following explanation, unless otherwise stated, deals with a G signal, but the explanation applies equally to R, B as well.
The portion indicated by A in FIG. 3 has a brightness signal level of 128. If this is represented in binary, a (1000 0000) signal level is added to each pixel in the portion indicated by A. Similarly, the portion indicated by B has a brightness of 127, and a (0111 1111) signal level is added to each pixel. The portion indicated by C has a brightness of 126, and a (0111 1110) signal level is added to each pixel. The portion indicated by D has a brightness of 125, and a (0111 1101) signal level is added to each pixel. The portion indicated by E has a brightness of 0, and a (0000 0000) signal level is added to each pixel. Lining up an 8-bit signal for each pixel perpendicularly in each pixel location, and horizontally slicing it bit-by-bit produces a subfield. That is, in an image display method, which utilizes the so-called subfield method, by which 1 field is divided into a plurality of differently weighted binary images, and displayed by temporally superimposing these binary images, a subfield is 1 of the divided binary images.
Since each pixel is represented by 8 bits, as shown in FIG. 2, 8 subfields can be achieved. Collect the least significant bit of the 8-bit signal of each pixel, line them up in a 10.times.4 matrix, and let that be subfield SF1 (FIG. 2). Collect the second bit from the least significant bit, line them up similarly into a matrix, and let this be subfield SF2. Doing this creates subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8. Needless to say, subfield SF8 is formed by collecting and lining up the most significant bits.
FIG. 4 shows the standard form of 1 field of a PDP driving signal. As shown in FIG. 4, there are 8 subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 in the standard form of a PDP driving signal, and subfields SF1 through SF8 are processed in order, and all processing is performed within 1 field time. The processing of each subfield is explained using FIG. 4. The processing of each subfield is comprised of setup period P1, write period P2, sustain period P3, and erase period P4. At setup period P1, a single pulse is applied to a holding electrode E0, and a single pulse is also applied to each scanning electrode E1, E2, E4 (There are only up to 4 scanning electrodes indicated in FIG. 4 because there are only 4 scanning lines shown in the example in FIG. 3, but in reality, there are a plurality of scanning electrodes, 480, for example.). In accordance with this, preliminary discharge is performed.
At write period P2, a horizontal-direction scanning electrode scans sequentially, and a prescribed write is performed only to a pixel that received a pulse from a data electrode E5. For example, when processing subfield SF1, a write is performed for a pixel represented by "1" in subfield SF1 depicted in FIG. 2, and a write is not performed for a pixel represented by "0."
At sustain period P3, a sustaining electrode (drive pulse) is outputted in accordance with the weighted value of each subfield. For a written pixel represented by "1," a plasma discharge is performed for each sustaining electrode, and the brightness of a predetermined pixel is achieved with one plasma discharge. In subfield SF1, since weighting is "1," a brightness level of "1" is achieved. In subfield SF2, since weighting is "2," a brightness level of "2" is achieved. That is, write period P2 is the time when a pixel which is to emit light is selected, and sustain period P3 is the time when light is emitted a number of times that accords with the weighting quantity.
At erase period P4, residual charge is all erased.
As shown in FIG. 4, subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8 are weighted at 1, 2, 4, 8, 16, 32, 64, 128, respectively. Therefore, the brightness level of each pixel can be adjusted using 256 gradations, from 0 to 255.
In the B region of FIG. 3, light is emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is not emitted in subfield SF8. Therefore, a brightness level of "127" (=1+2+4+8+16+32+64) is achieved.
And in the A region of FIG. 3, light is not emitted in subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, but light is emitted in subfield SF8. Therefore, a brightness level of "128" is achieved.
There are a number of variations of PDP driving signals relative to the standard form of PDP driving signal shown in FIG. 4, and such variations are explained.
FIG. 5 shows a 2-times mode PDP driving signal. Furthermore, the PDP driving signal shown in FIG. 4 is a 1-times mode. For the 1-times mode of FIG. 4, the number of sustaining electrodes comprising sustain period P3 in subfields SF1 through SF8, that is, the weighting values, were 1, 2, 4, 8, 16, 32, 64, 128, respectively, but for the 2-times mode of FIG. 5, the number of sustaining electrodes comprising sustain period P3 in subfields SF1 through SF8 become 2, 4, 8, 16, 32, 64, 128, 256, respectively, with all subfields being doubled. In accordance with this, compared to a standard form PDP driving signal that is a 1-times mode, a 2-times mode PDP driving signal can display an image with 2 times the brightness.
FIG. 6 shows a 3-times mode PDP driving signal. Therefore, the number of sustaining electrodes comprising sustain period P3 in subfields SF1 through SF8 becomes 3, 6, 12, 24, 48, 96, 192, 384, respectively, with all subfields being tripled.
By so doing, although dependent on the degree of margin in 1 field, it is possible to create a maximum 6-times mode PDP driving signal. In accordance with this, it becomes possible to display an image with 6 times the brightness.
Here, a mode multiplier is generally expressed as N times. Furthermore, this N can also be expressed as a weighting multiplier N.
FIG. 7(A) shows a standard form PDP driving signal, and FIG. 7(B) shows a variation of a PDP driving signal, which, by adding 1 subfield, comprises subfields SF1 through SF9. For the standard form, the final subfield SF8 is weighted by a sustaining electrode of 128, and for the variation in FIG. 7(B), each of the last 2 subfields SF8, SF9 is weighted by a sustaining electrode of 64. For example, when a brightness level of 130 is represented, with the standard form of FIG. 7(A), this can be achieved using both subfield SF2 (weighted 2) and subfield SF8 (weighted 128), whereas with the variation of FIG. 7(B), this brightness level can be achieved using 3 subfields, subfield SF2 (weighted 2), subfield SF8 (weighted 64), and subfield SF9 (weighted 64). By increasing the number of subfields in this way, it is possible to decrease the weight of the subfield with the greatest weight. Decreasing the weight like this enables pseudo-contour noise to be decreased, giving the display of an image greater clarity.
Here, the number of subfields is generally expressed as Z. For the standard form of FIG. 7(A), the subfield number Z is 8, and 1 pixel is represented by 8 bits. As for FIG. 7(B), the subfield number Z is 9, and 1 pixel is represented by 9 bits. That is, in the case of the subfield number Z, 1 pixel is represented by Z bits.
FIG. 8 shows the development of a PDP driving signal in the past. When a PDP driving signal changed from a certain field to the next field, if the subfield number Z changed, or the mode number N changed, the light emission center point of the subfield with the largest number of light emissions in each field (hereinafter referred to as the most-weighted subfield) moved.
Here, the light emission center point refers to the center point between the point in time of light emission start, which is the leading edge of sustain period for a certain subfield, and the point in time of light emission end, which is the trailing edge of sustain period for a certain subfield.
FIG. 8A shows a field, in which the subfield number Z is 12, and the light emission center point of the most-weighted subfield SF12 is C1. FIG. 8B shows a field, in which the subfield number Z is 11, and the light emission center point of the most-weighted subfield SF11 is C2. In general, light emission is performed sequentially from the subfield with the smallest number of light emissions to the subfield with the largest number of light emissions. Now, if it is assumed that a change is made from the field of FIG. 8A to the field of FIG. 8B, a time difference Td is generated between the time from the leading edge of the field of FIG. 8A to C1, and the leading edge of the field of FIG. 8B to C2. This time difference Td causes an unnatural fluctuation in image brightness.
Because the most-weighted subfield undertakes the largest number of light emissions for the field in which this subfield exists, it greatly effects the brightness of that field. The length of 1 field, for example, is 16.666 msec. If the light emission center points of the most-weighted subfields appear at the same cycle (for example, 16.666 msec) for a plurality of fields, this can be seen as a natural brightness change, but if the light emission center points of the most-weighted subfields appear as either contiguous or separate, a person viewing the screen will sense an unnatural brightness fluctuation.
The present invention proposes a PDP display drive pulse controller for preventing light emission center fluctuation, by which the light emission center point of a most-weighted subfield does not fluctuate even when a subfield number Z changes, and/or a mode number N, that is, a weighting multiplier N changes.